Geometric Limits of Foamed Glass Aggregate Fill behind Cantilever Walls and Abutments

Lightweight foam glass aggregate (FGA) has a low unit weight and high friction angle that, when used as a backfill behind walls and abutments, is expected to produce significantly lower earth pressures compared to conventional cohesionless fill soils. This paper describes a study performed to evaluate the minimum extent of FGA backfill required behind a wall or abutment to keep the theoretical earth pressure within 15% of the theoretical earth pressure from FGA fill alone. Three analysis methods were applied to determine the minimum dimensions of a trapezoidal prism of FGA backfill located between the wall and conventional soil or aggregate: (1) Coulomb planar surface analysis, (2) noncircular limit equilibrium (LE) analysis using Spencer’s method, and (3) plane strain strength reduction factor (SRF) analysis. These methods were applied in a parametric study that considered a range of values for the unit weight and friction angle for a cohesionless conventional backfill soil and FGA backfill located between the wall and the in situ conventional soil. Based on the analysis results, an empirical equation was developed for the maximum cut slope angle as a function of material properties and wall height.